1. The Field of the Invention
The present invention relates generally to optical devices in high-speed communication networks. More particularly, the present invention relates to systems and methods for measuring the turn-on and turn-off times of optical circuitry in an optoelectronic device.
2. The Related Technology
Devices such as optoelectronic transceivers include lasers and electronic elements that must be turned on and off rapidly in order to, for example, be used effectively in passive optical networks. Passive optical networks are described in Applicant's U.S. Provisional Patent Application Ser. No. 10/188,575, filed Sep. 5, 2002 and entitled “SYSTEM FOR CONTROLLING BIAS CURRENT IN LASER DIODES WITH IMPROVED SWITCHING RATES,” which is incorporated herein by reference.
Passive optical networks enable optoelectronic transceivers to share optical fibers while transmitting and receiving data in an optical form. Generally, a transceiver may not use all the bandwidth available on a fiber because data transmission is intermittent. As a result, transmitting and receiving data on optical fibers using more than one optoelectronic transceiver helps maximize the use of the network's bandwidth.
A passive network system utilizes the bandwidth available on a fiber by turning on a second transceiver when the first transceiver stops transmitting. Likewise, when the second transmitter finishes transmitting, another transmitter transmits data and so forth. Typically, passive optical networks employ a time division multiplexing access (TDMA) scheme to make this possible. In such schemes, the data transmission capabilities of the optoelectronic transceivers are operational only during separate, non-overlapping periods of time. Overlapping transceiver signals can cause unacceptable transmission errors in the passive optical network.
Because transceivers cannot transmit overlapping data, it is useful to ensure that a particular transceiver is completely off before the next transceiver begins transmitting data. However, when an optoelectronic transceiver receives a command to disable its optical transmitter circuitry, the response is not instantaneous. Instead, a measurable amount of time passes before the command is effectuated and the optical transmitter circuitry is turned off. Similarly, when an optoelectronic transceiver receives a command to enable its optical transmitter circuitry, the response time is also measurable. The amount of time required for turning optical transmitter circuitry on and off determines when a subsequent transmitter should be enabled to transmit data without causing an overlap in transmission with the first transceiver.
One method for ensuring that data does not overlap is to wait a predetermined period of time that is long enough to ensure that the first transceiver is not transmitting data when the subsequent transceiver begins transmitting data. However, this approach will likely result in unnecessarily long periods of time where the network is not transmitting data while it waits to ensure that the first transceiver has stopped. This approach fails to accomplish the object of utilizing as much of the network's bandwidth as possible.
Transceivers can make better use of network bandwidth by causing the subsequent transceiver to begin data transmission as soon as possible following the termination of data transmission by the first transmitter. Knowing the delay time for turning the transceiver on and off is useful for determining when a transceiver can be enabled without causing overlap in data transmission. By accounting for delay in the transceiver's turn-on and turn-off time, the transceiver can be configured to transmit data with much less delay between multiple transceiver transmissions than would otherwise be possible.